Introduction: User Profile Service Failed Logon Fix
I'm making this instructable because I ran into this problem myself and had a hell of a time finding out how to fix it. Surprisingly enough I couldn't even find it here. But now there will be a way. This is that way.
Step 1: Safe Mode Startup
First you need to start your computer in safe mode to do this you could either
a. while your computer is on hold the physical power button until it powers off, so that when you turn it back on it automatically pulls up the window in the first image.
or b. after correctly powering off your computer using the onscreen power off button. turn on your computer as it is booting press F8 repeatedly so that the screen of the first picture is pulled up
Once your computer shows the first image use the arrow keys to highlight "safe mode" and hit enter. You are now in safe mode.
Step 2: Find the Files
Once in safe mode click the start button to pull up the search bar that will show directly above it. In the Search bar type in Regedit and hit enter. (if you are propted for an administrator password type your password and click continue)
When the next window pops up locate the registry key 'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\ProfileLift.
To do this I had to find the first folder HKEY_LOCAL_MACHINE and click the expand icon beside it and repeat the process for each of the sections (Software, microsoft, windows nt, current version, and Profile lift)
Step 3: Edit the Names
1.After extending ProfileLift there should be some folders in the format S-1-5-XXXXX. Find the one with the ending ".bak" in the name, do this by hovering the mouse over the folders once found click on the one with .bak.
2.There should be another folder with the same sequence in the name except for this one doesn't have ".bak" Edit the last part of the name so that there is ".old" at the end of it.
3.Now right click on the one with ".bak" and remove the ".bak"
4.Right click on the ".old" folder and replace the ".old" with ".bak"
Step 4: Resetting the Count and State
Now left click on the folder without the ".bak"
1.In the left side of the window there should be several files. Right click on the "RefCount" file and chose "Modify" if the value in the window that pops up is anything but '0' then change it to '0' and click okay
2.Now right click on the file "State" and choose "modify". If the value in the window that pops up is anything but '0' then change it to '0' and click okay.
Step 5: Happiness
Close all windows and restart your computer in normal mode. Sign in and enjoy your reunion with your computer.